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Mikado Modellhubschrauber . GrandRC . Futaba-RC

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Main Discussion > Linear Servo travel analysis
 
 
serious_sam
Senior Heliman
Location: New York

some much simpler analyses

hi coleopter,

great calcs! however, some thoughts just came in. in trigonometry, sin (theta) is almost equal to tan (theta), which is also almost equal to (theta), in small displacements. the eventual travel at the bellcrank is something linked to this (theta).

this means that as long as the movement is small (usually within 10 degrees), the servo travel is pretty much "linear". outside this region, differential travels occur since the sine and tangent functions are no longer linear. i think this may be easier for people to understand without digging into the equations.

of course your calcs would still serve as the legitimate proof.

ps: for helis that use small servo ATV (like 3DNT) the travels would be pretty much linear!
04-09-2002 04:51 AM
 
 
steve9534
Key Veteran
Location: yakima, wa.

CCPM

Semi-articulate;
I'm afraid we aren't even talking the same language. When I said with ECCPM the servo movements are divided between collective and cyclic functions, I meant that the movement of each of the servos will affect both cyclic and collective functions. I think I'm saying the same thing as you were in a different way. The real point I'm trying to make is that the cyclic travel will be affected by the position of the collective, and cyclic sensitivity will be greatest at the center of the collective range and least at the extremes. I'm really at a loss to know how to explain the concept more clearly. Hope this helps. Steve.
04-09-2002 04:08 PM
 
 
steve9534
Key Veteran
Location: yakima, wa.

ECCPM

Maybe just one more stab at it, then I'll shut up. ECCPM using rotary servos gives a dual rate effect on the cyclic functions with low rate at full + or - collective, and high rate at center.
I probably should have started a new thread on this because this is really another issue apart from what was being discussed, and I think I just threw a monkey wrench in the works. Steve.
04-09-2002 09:01 PM
 
 
SemiArticulate
Veteran
Location: On Location

steve9534, I think I understand what you are getting at. I'll try to post a simulation of the system hopefully by this weekend.

alexander, yes I think it is more than twenty years old? Vario claims to have invented it. Not for performance exactly, but to squeeze the control system into a scale fuse and still leave room for a cockpit etc.
04-09-2002 10:00 PM
 
 
steve9534
Key Veteran
Location: yakima, wa.

CCPM

Semi-articulate;
I just wanted to say that it's a pleasure having these discussions with someone who is indeed articulate and doesn't immediately lapse into an angry dispute when we don't understand something exactly the same. Thanks. Steve.
04-10-2002 07:00 AM
 
 
SemiArticulate
Veteran
Location: On Location

Thanks a lot. Although I have noticed after reading and being involved in several topics that keeping a good discussion is a group effort. I have found myself in the middle of some strange topics so I know what your talking about . This topic gets more involved since it is not like we are standing around a table and able to pass each other drawings and sketches. That would make it much easier to convey our ideas. Hopefully I can generate some helpful computer models pretty soon. I have several projects I need to get out of the way first. Not the most important (but most important to me) is adding some upgrades to my helis before this weekend .
04-10-2002 10:46 PM
 
 
SemiArticulate
Veteran
Location: On Location

I have had a chance to fool around with the modeling program. I am only using the 2D version now. It may take a little longer to do this since I need to re-learn some of the interface. I am modeling the MA part now but I think I have spotted another problem. The control rod moves parralel to the boom and is locked into this axis near the servo. So in order for the other end to follow then bellcrank, the control rod must bend (deflect) just a little to follow the path of the arc on the tail rotor end? My software does not understand that material can bend and models the ideal kinematics. I guess I will rig up some 'bender' joint to get around this.
04-14-2002 02:09 AM
 
 
SemiArticulate
Veteran
Location: On Location

I've not forgotten to make the computer models. I have just had bigger fish to fry. I'll post more on that latter. Hard to schedule anything this time of year unless you know it will be raining.
04-22-2002 03:11 AM
 
 
Heli genius
Senior Heliman
Location: Hong Kong

From my point of view linear input and linear output is good. However, this doesn't matter for me as the key point is you have to get the feeling that you are the pilot inside of the heli and you have the feeling of the response without reluctant. The minor exp or non linear should not affect you. In fact, your finger is also not moving in linear motion, your finger have many pivot and this is unavoidable.
11-05-2003 10:37 AM
 
 
PPLON
Senior Heliman
Location: Mexico City

just subscribing to this interesting topic for further reference
thanks guys.


03-26-2005 01:49 AM
 
 
Wayne Mann
Senior Heliman
Location: United States of America

After reading this I thought that I would add a couple things to the thread.

First Stephen I agree with you 100%. ECCPM is a manufactures dream. A whole lot less parts, BUT sell the helicopter for more money and bill it as the latest and greatest thing.

I bit of trivia. Did you guys know that Curtis is the only pilot to ever win a World Championship with ECCPM. All of the other winners were using MCCPM in various forms.

I still maintain that ECCPM is better for 3D for a couple of reasons. The first and most obvious reason is that there are much fewer expensive aluminum parts to bend or break in a crash and God knows those guys tear up some helicopters. Second, ECCPM has quite a bit more control power for cyclics and collective than mechanical mixing. I have tested and proven this with my Calibers.

In the beginning of this thread there were a couple of questions asked about 140 degree ECCPM that I don't think were answered. 140 degree ECCPM eliminates two major problems. First, you now have all three servos operating with the same resolution and second, it gets rid of the swash plate ball bouncing up and down when you operate fore and aft cyclic fairly fast which is due to the pitch and aileron servo getting to their destination sooner than the elevator servo. 140 degree ECCPM does NOT get rid of the cyclic interactions that accure at high and low collective settings however. BUMMER!!! Nor does it fix the problem of getting 3 servos to track together perfectly. BUMMER!!!

Since Futaba now has a radio that is capable of 140 degree ECCPM I think that ALL manufactures of 60 to 90 size helicopters should offer 140 degree ECCPM due to the two problems with 120 degree ECCPM that I listed above. From a practical and common since stand point, I just don't get 120 degree ECCPM. Ewald Heim and Vario or whoever origionally developed this system should have seen the major flaw in their design and corrected it. If they had I feel very confident that there would not be machines available today with 120 degree ECCPM.

I don't think everybody understands what some of these guys are talking about when they describe linear output from the servo. Linear output from a rotary servo basically means if you move the fore and aft cyclic stick from top to bottom at a steady speed the center of the pushrod that is connected to the servo wheel will travel from one end of it's range to the other at a steady speed. With a Futaba 9Z radio about -16% expo is required to achieve this as you need to slow the servo down while it's in the middle of it's travel range. But even with rotary servos adjusted to throw linear they still develop all kinds of funky angles and interactions at their extreme angles of throw. For ECCPM to develop or evolve into greatness we have to get rid of round servo wheels and bell cranks.

In order for ECCPM to reach that state of total creaminess in MY opinion the servos would have to be mounted underneath the swash plate with no bell cranks and the servos would have a straight shaft sticking out of them with a ball threaded in the end to hook the pushrod to. This would eliminate ALL and I mean ALL cyclic interactions at high and low collective settings assuming that none of the servos run out of travel. We all know what happens when we make assumptions. What is assumption after all...The Mother of all F_ _k ups. The major obstacle that would have to be overcome is the amount of throw that would be required from the servo that I described. It would have to be one long servo.

Wayne Mann
03-26-2005 05:40 AM
 
 
KC
Elite Veteran
Location: WA

Wayne, you fly eccpm calibers still?

just curious why you fly eccpm now over other mechanical machines available?
03-26-2005 05:52 PM
HOMEPAGE  
 
 
Dr.Ben
Elite Veteran
Location: Richmond, VA, USA

When you're a professional pilot and consultant, you often have to work with the product made by the company that is putting food on your table. That's the reality of the situation.

Ben Minor
03-26-2005 06:06 PM
 
 
Wayne Mann
Senior Heliman
Location: United States of America

Hi KC. I actually have a couple of Calibers with mechanical mixing. I haven't converted the rest in hopes that the new Futaba radio will solve most of my issues.

Wayne Mann
03-26-2005 06:55 PM
 
 
AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

One can calculate till the cows come home and it can be interesting.

But in the end, setup your linkages reasonably close to 90º at center travel, use a bit of expo on cyclic and call it good.

The rest is just plain 'ole flying skills. The brain does a wonderful job of compensation through eye-hand coordination.

Wolfgang
03-27-2005 12:10 AM
HOMEPAGE  
 
 
KC
Elite Veteran
Location: WA

thanks Wayne!
03-27-2005 05:06 AM
HOMEPAGE  
 
 
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Main Discussion > Linear Servo travel analysis
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